Well, should have looked a bit longer I guess...
There it was, under the Files drop-down menu - you call it "New Diff", and yes, you load two files in and the differences show up as another colour.
May I suggest that you have this info in the Help file?
'New Diff' works exactly as I wanted, just a bit more buried than I could casually find 'casue I was looking for "Compare'!.
Great program!